Phase Matchability Transformation in the Infrared Nonlinear Optical Materials with Diamond‐Like Frameworks

Abstract Phase matchability is a prerequisite for infrared nonlinear optical (IR‐NLO) crystals. Hitherto, it is relatively infrequent to design and synthesize phase‐matching (PM) materials from known non‐phase‐matching (NPM) materials. This work reports a series of PM chalcogenides AM^II₃Ga₅S₁₁ (A = K, Rb, Cs; M^II = Cd, Mn) with diamond‐like frameworks (DLFs), which are derived from the known NPM AM^II₄Ga₅S₁₂ in the A₂S−M^IIS−Ga₂S₃ pseudoternary diagram. Notably, ACd₃Ga₅S₁₁ and AMn₃Ga₅S₁₁ are isomeric and exhibit different DLFs and remarkable overall properties. Especially, KCd₃Ga₅S₁₁ achieves the coexistence of wide band gap (E_g = 3.25 eV), strong second‐harmonic‐generation (SHG) response (1.7 × benchmark AgGaS₂) and ultrahigh laser‐induced damage threshold (36.5 × benchmark AgGaS₂), which is the best IR‐NLO chalcogenides with DLF known to date. Theoretical calculations reveal that their superior performance and PM behavior are benefited from the anisotropic structural characteristics, i.e., DLFs. This work demonstrates the feasibility of designing PM IR‐NLO materials via the partial removal of asymmetric building blocks in DLF structures of NPM materials that is accessible and controllable by chemistry means.